This invention relates to a pipeline plug or packer for plugging a pipeline, such as a crude oil pipeline, at a selected location therealong.
Pipeline packers of the type to which the present invention relates are designed to act as positionable shut-off valves inside a pipeline. The packer is typically loaded into the pipeline through a standard pig trap and the packer is transported along the pipeline by the fluid flowing in the line. Tracking of the packer is typically done from above ground with a sensor receiving signal from a transmitter located on the packer. When the packer reaches the desired position, the pipeline pumping equipment is stopped to stop the flow and the packer is activated by remote control so as to seal the pipeline at that location. With two packers spaced some distance apart, it is possible to isolate a section of the pipeline, thereby allowing that section of the pipeline to be drained to provide a substantially liquid-free environment without draining the entire line. After the desired work in the pipeline has been accomplished, the packer is released by remote control, and the flow through the pipeline is started up to move the packer along the line with the packer being thereafter removed through a further pig trap.
The pipeline packer must be capable of forming a reliable seal under a wide variety of conditions. In mountainous country, extremely high pipeline hydrostatic heads are common, typically being in the order of several hundred pounds per square inch and, in extreme cases, pressure heads as high as 1000 pounds per square inch may be encountered.
The prior art devices typically fall into two main categories. The first category of packer employs one or more inflatable annular cuffs which are expanded outwardly into contact with the pipeline interior wall in an effort to resist the pressures developed during use. Packers employing inflatable cuffs are not effective in providing a seal at high pressures as the cuff material is incapable of tightly gripping the pipeline interior wall (which wall may have an accumulation of waxy material or other deposits thereon reducing the co-efficient of friction obtainable) with the result being that packers of this nature tend to be moved fairly quickly out of their intended positions. The other category of packer typically employs a plurality of wedge-shaped shoes or slips which may be activated by hydraulic pressure to bring such shoes into gripping engagement with the pipeline interior wall. Auxiliary sealing means for engaging the pipeline interior wall are also provided to prevent leakage of fluid. Again, difficulties have been encountered with these arrangements owing to the fact that the gripping shoes tend to bite into and damage the pipeline interior wall. This damage opens the way for rapid corrosion owing to the presence of sulphur compounds in the crude oil being pumped. In addition, the roughening of the pipeline interior wall is strongly objected to by most pipeline companies since this roughness tends to damage the annular seals or rubbers which are used in conjunction with pipeline cleaning pigs and the like which are caused to travel along the pipeline interior at regular intervals. Reliability of the prior art devices has also been a factor with certain of the wedge or slip type arrangements having been known to jam in the gripping and sealing position thus giving rise to serious difficulties. Many of the prior art devices were also rather bulky and cumbersome, many requiring external sources of electrical and hydraulic power thus necessitating the use of extremely long lengths of hydraulic lines and electrical conduits.